Gas turbine engines include several compressed air plenums and ducts for conducting pressurized air for cooling over various engine components. The complexity of manufacturing and assembly of various components represents a significant cost factor in the production and maintenance of aircraft engines. In general, it is preferable to replace multiple parts with single cast or machined parts to reduce the complexity of manufacturing.
The present invention is directed to the manufacture and assembly of a circumferential array of stator blades with outer shroud and inner shroud. The stator array is positioned between the high pressure compressor turbine and the low pressure compressor turbine immediately downstream of the combustor. Between these two turbines is the circumferential array of stator blades which include a radially inwardly directed conduit to conduct cooling air from a plenum surrounding the combustor into the interior of the engine for accumulation in a T.O.B.I. feed plenum. From the T.O.B.I. plenum, cooling air is directed toward the cover plate and body of the low pressure compressor turbine. The T.O.B.I. plenum includes nozzles directed toward the cover plate and turbine to direct cooling air on and through the cover plate and turbine.
Conventional designs of stator arrays generally include multiple components which are assembled together into a ring like structure. Individual stator blades are machined and assembled together into a ring structure during manufacture. In general, if any machined components can be manufactured in a single unit, costs and labour savings result. Recently the capability of accurately machining large metal parts has increased through use of computer-aided manufacturing and computer numerical controlled machining. CAD and CNC enable designers to combine extremely complex components together into a single part. The complex geometry of blade shapes and geometry of the hot gas path have in the past resulted in manufacturing procedures which include individually machining each stator blade then brazing the blades together with the outer and inner shrouds to define the hot gas path.
It is desirable to produce a stator blade assembly in a single ring-like unit. For ease of manufacture and maintenance of structural integrity, it is desirable to produce a single ring-like structure utilizing the outer shroud as a continuous hoop member, whereas the blades and attached inner shrouds are split apart. Splitting the inner shroud allows for relieving of internal stresses, facilitates fabrication of the ring structure, facilitates inspection and simplifies maintenance. Fabrication can involve unitary casting of the one-piece outer shroud together with split inner shroud and radial stator blades, or machining individual stator blades then brazing the individual stator blades to form an integral outer shroud and split inner shroud.
The individual stator blades with attached inner shroud segments must be joined together into an inner annular shroud in a manner which maintains the seal of the inner shroud preventing air from escaping from the T.O.B.I. plenum into the hot gas path. Leakage of cooling air would result in a significant decrease in the efficiency of the engine cooling system.
Therefore, it is very desirable to provide a split inner shroud that can be efficiently sealed to prevent migration between the hot gas path and the cooling air within the plenum. It is also highly desirable to produce a plenum from easily assembled and disassembled components that can be inspected, replaced or repaired during routine maintenance.